In the continuous or semi-continuous casting of molten aluminum or other metal ingots there is a desire to increase the rate at which ingots are cast or withdrawn from the mold or casting device both to improve production rate and to improve the surface condition of the ingot so produced. Many attempts have been made to accomplish such, but have often been marked by a propensity to form cracks in the ingot wherein a higher casting rate produces better production rates but higher rejection rates because of ingot cracks. Another problem is that some retarded chill rate systems used to reduce cracks result in internal porosity which reduces the usefulness of the solidified metal.
U.S. Pat. No. 3,713,479, incorporated herein by reference, addresses this type of problem to some extent and relies upon different cooling zones. Similarly, U.S. Pat. Nos. 3,463,220 and 3,726,336, incorporated herein by reference, are concerned with the reduction of ingot cracks in producing ingots at relatively high production rates employing air and water-cooling mixtures. The various methods employed to date each are considered to have shortcomings either insofar as the results achieved or difficulty in control or in implementation of the system.